complete dark for plants is recomended. star light is too far away and travels through cold space. its usable spectrum is absorbed by space as it travels, star light only arrives on earth one photon at a time. not usable for plants- moonlight is relected sunlight but is not the same as light being relected off your MH or HPS hood. It has something to do with the moon is not being smooth and the reflected light looses a majority of its spectrum if it isnt from a "pure" source. some degree of light has to be ok. where that degree is, i dont know. all i know is for the time and effort i put into this i wouldnt let a firefly or a nite light near my plants after lights out. out of all the things you have to control to grow successfuly (light, heat, nutrients, PH, watering schedules, RH) getting it dark when it is supposed to be has to be the easiest by far.